In manufacturing semiconductor devices, a mask with a desired pattern is formed on a substrate to be processed. The mask may be a multilayer mask made of a multilayer film including a resist film, a Si anti-reflection coating film, i.e., a SiARC (Anti Reflection Coating) film, and an organic film. In order to form the multilayer mask, the organic film, the SiARC film and the photosensitive resist film are formed on the substrate to be processed. Then, a resist mask is formed by exposing and developing the resist film to have a pattern. Next, the SiARC film and the organic film are etched.
As for a method for forming such a multilayer mask in a desired pattern, there is used a method for realizing pattern size accuracy by suppressing excessive etching on a sidewall of the multilayer mask by depositing by-products generated during the etching on the sidewall defining a space formed by the etching. A sidewall protection technique using by-products is disclosed in, e.g., Patent Document 1. However, the sidewall protection technique using by-products requires a complicated process or condition management in order to uniformly control the deposition amount of by-products over the entire sidewall, as disclosed in Patent Document 1.
Recently, methods using COS (carbonyl sulfide) gas as an additional gas which are disclosed in Patent Documents 2 and 3 are suggested as a sidewall protection technique during etching. Specifically, in the method disclosed in Patent Document 2, a parallel plate type plasma etching device etches a SiARC film by using a gaseous mixture of CF4 gas and COS gas. Further, in the method disclosed in Patent Document 3, after a SiARC film is etched in the method of Patent Document 2, the parallel plate type plasma etching device etches an organic film by using a gaseous mixture of O2 gas and COS gas.